Cambridge IGCSE·Co-ordinated Sciences 0654·Chemistry Chemical Formulae

📋Key knowledge — Stoichiometry

Formulas & equations

Moles = mass (g) ÷ molar mass (g/mol)
Moles = volume (dm³) × concentration (mol/dm³)
Moles of gas at RTP = volume (dm³) ÷ 24 (at room temperature and pressure)
% yield = (actual yield ÷ theoretical yield) × 100
% purity = (mass of pure substance ÷ total mass) × 100
Empirical formula: simplest whole-number ratio of atoms. Molecular formula: actual ratio.

Key facts & rules

Avogadro's number: 1 mole contains 6.02 × 10²³ particles.
Molar mass: sum of Ar values from the periodic table for one formula unit.
Balancing equations: atoms must be equal on both sides — only coefficients can change, not formulae.
Limiting reagent: the reactant that runs out first, determining the maximum yield.
Excess reagent: the reactant that is not used up.

IGCSE Chemistry — Chemical formulae

5 Cambridge IGCSE 0654 questions on chemical formulae, across all three components.

About chemical formulae on IGCSE 0654

Every Cambridge IGCSE Co-ordinated Sciences 0654 question on chemical formulae (Stoichiometry, Chemistry), across all three exam components. Theory and alternative-to-practical come with full mark schemes; multiple choice is interactive — click an option to check it.